A touch screen can be used in electronic devices, such as cellular phones, tablet personal computers, and e-readers. The touch screen displays static images or motion graphics. A light source is equipped in the electronic device to backlight the touch screen. To control the electronic device, a user can enter his control commands by touching a display area of the touch screen with his finger, hand or stylus. The touch screen includes touch sensors for detecting the presence and the location of the user's touch.
FIG. 1 illustrates a block diagram of a conventional display system 100. The display system 100 includes a light source 112 that backlights a touch screen (not shown) and further includes touch sensors 122 within the display area of the touch screen. The display system 100 further includes converters such as a converter 108 and a converter 114, a power source 102, a DC/DC converter 104, a filter 118, a level shifter 120, a converter controller 110, and a converter controller 116.
The converter 108 and the converter 114 are operable for driving the light source 112 and the touch sensors 122, respectively. More specifically, the power source 102 generates an input voltage VIN. The application processor 106 generates reference signals 124, 128 and 130, and further generates an input clock signal CLK_IN. The converter 108 receives the input voltage VIN and provides an output voltage VOUT1 to power the light source 112. The converter controller 110 coupled to the converter 108 receives the reference signal 124 indicating a desired current level for the current flowing through the light source 112. Accordingly, the converter controller 110 generates a control signal 150 to regulate the output voltage VOUT1. Thus, the current flowing through the light source 112 is adjusted to the desired current level.
The converter 114 receives the input voltage VIN and provides an output voltage VOUT2. The converter controller 116 coupled to the converter 114 receives the reference signal 130 indicating a desired voltage level for the output voltage VOUT2. Accordingly, the converter controller 116 generates a control signal 152 to regulate the output voltage VOUT2. The filter 118 filters the output voltage VOUT2. The level shifter 120 receives the input clock signal CLK_IN and provides an output clock signal CLK_OUT according to the output voltage VOUT2 to drive the touch sensors 122. The frequency of the output clock signal CLK_OUT is equal to the frequency of the input clock signal CLK_IN. Moreover, the low electrical level of the output clock signal CLK_OUT is approximately equal to zero volts, and the high electrical level of the output clock signal CLK_OUT is approximately equal to the output voltage VOUT2.
The converter controller 116 further receives the reference signal 128 indicating whether the touch sensors 122 are required to be turned off. If the reference signal 128 is active, the converter controller 116 regulates the output voltage VOUT2 to zero volts to switch off the touch sensors 122.
However, the converter 108, the converter controller 110, the converter 114, and the converter controller 116 increase the size and the cost of the display system 100. Moreover, each of the reference signals 124, 128 and 130 is transferred on a respective line to another component. As such, the multiple lines increase the complexity and the cost of the display system 100.